It is well established that memory T cells preferentially migrate to the skin. However, it is not known whether skin-seeking memory T cells are a specialized subpopulation of all memory cells or whether memory T cells generally migrate to all tissues at the first line of defense, including the skin. If a skin-seeking memory T cell subpopulation exists, the generation of such memory cells may depend on the microenvironment in lymph nodes that drain the skin. We will test this possibility in Aim 2. Alternatively, all memory cells that provide cell mediated immunity (T helper 1 cells) may preferentially migrate to the skin, where they perform tissue surveillance, while memory T cells that provide B cell help (T helper 2 cells), may migrate to lymphoid tissues instead. Aim 2 tests this possibility. We will use a new approach to monitor memory T cell migration involving adoptive transfer of T cell receptor (TCR) transgenic T cells into normal syngeneic mice. Thereby, a clonal population of T cells with a defined history of antigen experience can be followed by means of a clonotypic marker, the transgenic TCR molecule. The density of TCR-T cells in various tissues, including the skin, as established by immunohistochemistry, provides a direct measure of T cell migration to those tissues. Since the TCR+T cells from the transgenic mouse retain their naive state in the adoptive host, we can establish the tissue distribution of naive T cells in unimmunized chimeras, establishing to what extent naive T cells frequent extra-lymphoid tissues and the skin (Aim 1). Subsequently, we will convert the naive TCR+T cells into the memory cells using the subcutaneous or systemic route for immunization. Thereby we can test whether differentiation of memory T cells in skin-draining lymph nodes biases memory cell differentiation toward a skin-seeking memory T cell population (Aim 2). Finally, we will apply immunization protocols that generate either pro-inflammatory T helper 1 (Th1) cells, whose primary function is cell mediated immunosurveillance, or T helper 2 cells that provide B cell help, promoting humoral immunity via specific antibody production. This permits us to test the whether functional constraints direct memory cell migration: do Th1 cells have to migrate to the first line of defense to provide immune surveillance while Th2 cells have to migrate to lymphoid tissues to provide T cell help? Hence, do Th1 and Th2 cells migrate differentially (Aim 3)?